1. Field of the Invention
Embodiments described herein relate generally to a current regulation method of multiple beams and, for example, relate to a technique of regulating a current when a pattern is written by irradiating a target object on a stage with multiple beams.
2. Related Art
A lithography technology taking charge of advancing micropatterning of semiconductor devices is an extremely important process that, among semiconductor manufacturing processes, solely generates a pattern. With ever higher integration of LSI in recent years, circuit line widths demanded for semiconductor devices become finer year by year. Here, the electron beam writing technology has essentially excellent resolving power and writing on a wafer is performed by using an electron beam.
For example, a writing apparatus using multiple beams is available. Since irradiation of many beams can be performed at a time by using multiple beams, when compared with a case of writing with one electron beam, throughput can significantly be improved. In such a writing apparatus of the multiple beams mode, for example, multiple beams is formed by passing an electron beam emitted from an electron gun assembly through a mask having a plurality of holes and each is blanking controlled and a desired position on a target object is irradiated with each beam that is not blocked (see Published Unexamined Japanese Patent Application No. 2006-261342, for example).
In an electron gun assembly of thermionic emission type used for electron beam writing, a cathode material evaporates during operation. Thus, the shape of the cathode material changes with time and under the influence thereof, the current density distribution of an electron beam with which a target object is irradiated also changes with time. Therefore, the amount of current of each beam of multiple beams changes with time. The amount of current of each beam is conventionally measured before writing and the irradiation time (exposure time) of each beam is determined based on the measured amount of current. However, as described above, if the writing time becomes longer with degradation of the cathode material by the passage of time, an error arises in the exposure time of each beam. Therefore, there has been a problem of deteriorating dimensional accuracy of a written pattern.
In electron beam writing of the single beam mode, though not multiple beams, a technology of regulating a bias voltage or the like so as to maintain a current density by measuring the amount of current of the whole single beam reaching a target object to acquire the current density is disclosed (see Japanese Patent No. 4676461, for example).